China said it has filed a protest with Japan over Tokyo's plan to name uninhabited isles near the disputed Senkaku Islands in the East China Sea, calling the move "illegal and void."

Foreign Ministry spokesman Liu Weimin said Monday the Chinese government has lodged a "solemn representation" with Japan.

"Any unilateral action taken by the Japanese side with respect to the Diaoyu Islands and surrounding isles is illegal and void," Liu said in a press release posted on the ministry's website.

The Japan-administered Senkakus are known in China as Diaoyu. It is not clear what name Japan intends for any nearby islets.

In an opinion piece published earlier in January, the state-run People's Daily newspaper called the islets part of Beijing's "core interest."

Japan's plan to name uninhabited nearby islands "is a blatant move to damage China's core interests," the newspaper said.

The Chinese government, however, has never officially said the islets, held by Japan but claimed by both China and Taiwan, represent Beijing's core interests.

In contrast, Beijing routinely uses that phrase to describe Taiwan and Tibet.

Relations between Japan and China deteriorated to their lowest point in years after Japan in 2010 arrested the captain of a Chinese trawler following collisions with Japanese patrol vessels near the Senkaku Islands.